CPNE4 (copine 4) is a calcium-dependent phospholipid-binding protein that functions as a membrane adaptor in calcium-mediated intracellular processes 1. The protein is particularly enriched in retinal ganglion cells (RGCs), where its expression is transcriptionally regulated by Brn3 transcription factors and restricted to specific RGC populations 12. When overexpressed, CPNE4 induces formation of large varicosities on RGC dendrites and can promote elongated process formation reminiscent of neurites in non-neuronal cells 12. Protein interaction studies reveal CPNE4 associates with over 200 proteins involved in metabolic and signaling pathways, including Host Cell Factor 1 and Morn2 1. Beyond the retina, CPNE4 shows broader physiological relevance, with genetic variants associated with muscle glycogen metabolism in chickens 3, migratory timing in birds through modulation of biological clock pathways 4, and age-related hearing loss susceptibility in mice 56. Additionally, CPNE4 5-hydroxymethylcytosine modifications in circulating cell-free DNA show potential as biomarkers for late-onset Alzheimer's disease diagnosis 7. These findings suggest CPNE4 functions as a calcium-sensing membrane adaptor with roles in neuronal morphogenesis, metabolism, and circadian regulation.